Constify data structures

Constify more data structures. Make functions static.

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
diff --git a/extensions/libxt_sctp.c b/extensions/libxt_sctp.c
index 2768ca5..634862b 100644
--- a/extensions/libxt_sctp.c
+++ b/extensions/libxt_sctp.c
@@ -110,7 +110,7 @@
 };
 
 /*'ALL' and 'NONE' will be treated specially. */
-static struct sctp_chunk_names sctp_chunk_names[]
+static const struct sctp_chunk_names sctp_chunk_names[]
 = { { .name = "DATA", 		.chunk_type = 0,   .valid_flags = "-----UBE"},
     { .name = "INIT", 		.chunk_type = 1,   .valid_flags = "--------"},
     { .name = "INIT_ACK", 	.chunk_type = 2,   .valid_flags = "--------"},